MySQL计算特定值的列

I have the following db table, and I would like to be able to count the instance of sales of certain products per salesperson.

我有以下数据库表，我希望能够计算每个销售人员的某些产品的销售实例。

|------------|------------|------------|
|id          |user_id     |product_id  |
|------------|------------|------------|
|1           |1           |2           |
|2           |1           |4           |
|3           |1           |2           |
|4           |2           |1           |
|------------|------------|------------|

I would like to able to create a result set like the following;

我想能够创建如下的结果集;

|------------|-------------|------------|------------|------------|
|user_id     |prod_1_count |prod_2_count|prod_3_count|prod_4_count|
|------------|-------------|------------|------------|------------|
|1           |0            |2           |0           |1           |
|2           |1            |0           |0           |0           |
|------------|-------------|------------|------------|------------|

I am creating graphs with this data, and once again (as earlier today) I am unable to count the column totals. I have tried;

我正在使用这些数据创建图表，并且再次（如今天早些时候）我无法计算列总数。我努力了;

SELECT user_id, 
(SELECT count(product_id) FROM sales WHERE product_id = 1) AS prod_1_count,
(SELECT count(product_id) FROM sales WHERE product_id = 2) AS prod_2_count,
(SELECT count(product_id) FROM sales WHERE product_id = 3) AS prod_3_count,
(SELECT count(product_id) FROM sales WHERE product_id = 4) AS prod_4_count 
FROM sales GROUP BY user_id;

I can see why this doesn't work, because for each bracketed SELECT the user_id doesn't match the external user_id in the main SELECT statement.

我可以看到为什么这不起作用，因为对于每个括号中的SELECT，user_id与主SELECT语句中的外部user_id不匹配。

Can anyone help out me here?

有人可以帮帮我吗？

thanks you

谢谢

3 个解决方案

#1

You can do this using SUM and CASE:

您可以使用SUM和CASE执行此操作：

select user_id,
  sum(case when product_id = 1 then 1 else 0 end) as prod_1_count,
  sum(case when product_id = 2 then 1 else 0 end) as prod_2_count,
  sum(case when product_id = 3 then 1 else 0 end) as prod_3_count,
  sum(case when product_id = 4 then 1 else 0 end) as prod_4_count
from your_table
group by user_id

#2

You are trying to pivot the data. MySQL does not have a pivot function so you will have to use an aggregate function with a CASE expression:

您正在尝试转动数据。 MySQL没有pivot函数，所以你必须使用带有CASE表达式的聚合函数：

select user_id,
  count(case when product_id = 1 then product_id end) as prod_1_count,
  count(case when product_id = 2 then product_id end) as prod_2_count,
  count(case when product_id = 3 then product_id end) as prod_3_count,
  count(case when product_id = 4 then product_id end) as prod_4_count
from sales
group by user_id;

See SQL Fiddle with Demo

请参阅SQL Fiddle with Demo

#3

See if this works:

看看这是否有效：

SELECT a.user_id, 
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 1 AND a.user_id = b.user_id) AS prod_1_count,
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 2 AND a.user_id = b.user_id) AS prod_2_count,
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 3 AND a.user_id = b.user_id) AS prod_3_count,
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 4 AND a.user_id = b.user_id) AS prod_4_count 
FROM sales a GROUP BY a.user_id;

Cheers. n.b. there may be slightly nicer ways to achieve the equivalent result.

干杯。注：可能会有更好的方法来实现相同的结果。

#1